Ground Improvement at US 101/Broadway Interchange Reconstruction Project-PPT Presentation

PPT Presentation

Pdf Summary

The US 101 Broadway Reconstruction project replaced a 1949 overcrossing with a two-span bridge, new and reconfigured ramps, and retaining walls supporting the approaches and ramps.

Ground conditions included fill over soft, compressible Young Bay Mud, with high seismicity and liquefaction-susceptible deposits. Retaining-wall settlement was therefore a key design concern. The presentation compares three mitigation approaches:

- <strong>Preloading with wick drains</strong> to accelerate consolidation: a well-established method, but it requires space for staging and a settlement period exceeding 120 days, with potential differential settlement.
- <strong>Lightweight embankment material</strong>: avoids a settlement waiting period, but loads on the wall remain a concern, and EPS blocks may require long-term maintenance.
- <strong>Deep soil mixing (DMM)</strong>: mixes cement with in-place soil to create soil-cement columns that increase strength and reduce compressibility. It avoids a settlement waiting period and was an established ground-improvement technique, though its application was relatively new for Caltrans.

The presentation emphasizes that the best solution is not always obvious: conventional options may be safe, while less conventional applications can involve greater risk. Successful delivery depends on research and a trusted team—including the designer, contractor, review agency, and client—and, ultimately, a willingness to take a considered leap of faith.

Keywords

US 101 Broadway Reconstruction

two-span bridge

retaining walls

Young Bay Mud

liquefaction

preloading with wick drains

lightweight embankment

deep soil mixing

ground improvement

seismicity